Diffusion MRI
is a technique for studying various aspects of microscopic tissue composition
and organization in the central nervous system (CNS). The diffusion time is a
key parameter to determine restricted diffusion in microstructures and hence
the sensitivity of diffusion MRI to different spatial dimensions. However, it
is not straightforward to implement pulsed gradient spin echo (PGSE)
diffusion experiments with short diffusion times that are needed to highlight
structures at microscopic scales. One alternative is to use oscillating
gradient spin echo (OGSE) or the so-called temporal diffusion spectroscopy,
which allows short diffusion time better than PGSE sequence, to provide a
unique way to measure water diffusion. Diffusion spectrum imaging (DSI) is
one of the diffusion MRI techniques that can map complex fiber architecture
in the brain. We sought to apply OGSE DSI to identify minuscule
neuroarchitecture in the brain. By applying oscillating diffusion-sensitive
magnetic gradients to tag translational motion of water molecules, 3D
probability density function (PDF) of molecular displacement can be
reconstructed from the measured OGSE DSI data. For comparison, diffusion tensor
images (DTI) of the rat brain were acquired using the OGSE and PGSE
sequences. We demonstrate DSI maps with oscillating gradient revealed novel
tissue contrast in the rat hippocampus.